1. Field of the Invention
The present invention relates to a swage fastening tool and in particular, to components of the tool which simplify its triggering function and provide improved valve damping characteristics.
2. Description of the Related Art
Conventional hand-held swaging tools typically include a cylindrical housing provided with an anvil at one end and a reciprocating piston movable within the housing towards and away from the anvil. The piston is provided with a coupler by which the pinshank of a swage-type fastener is gripped as it passes through the anvil. When the piston is moved away from the anvil, the collar of the fastener is drawn against the anvil and is swaged. After this occurs, the pinshank is designed to break so as to separate from the collar. The piston then reverses its direction and moves towards the anvil until it reaches a "home" position from which the swaging operation can be repeated.
The cylindrical housings of conventional hand-held swaging tools generally are joined with a handle through which fluid moves so as to selectively operate the piston in response to actuation of a trigger provided in the handle. When the trigger is actuated, a flow control valve is displaced to cause pressurized fluid to be applied to the piston to initiate the swaging operation, and when the pinshank breaks and the trigger is released, the valve operates to relieve pressure on the piston allowing it to return to its "home" position. The handle is disposed substantially perpendicular to the longitudinal axis of the piston-containing cylinder. Thus, it is necessary that means be provided to actuate a valve having a path of movement which differs up to 90.degree. from the direction of force applied to the valve-actuating trigger.
In some prior art devices this is accomplished by the use of air piloted valves which are combined with the trigger to initiate valve movement to actuate the tool's piston. However, air piloted valves require more seals than a directly operated valve and are more expensive. Additionally, such a piloting system requires the drilling of air passages which add to the complexity and machining cost of the tool.
Other trigger-operated valve arrangements utilize a crank-slider arrangement between the trigger and the valve. This requires a precision bore in the tool which is expensive to machine. Additionally, such an arrangement adds weight to the tool and is difficult to assemble.
Another type of arrangement uses a trigger lever, a cable and a second lever to interconnect the trigger to the valve. Such a linkage involves a number of parts and significant assembly time thereby rendering the arrangement a costly one.
A further shortcoming of known swaging tools resides in the complexity of providing a damping function to absorb the shock encountered when the pinshank of the fastener breaks and the direction of piston movement reverses. This problem is addressed in conventional tools by providing a damper valve in the path of fluid flow which has one or more passages which are opened when the fluid flows in a first direction, and a passage or passages of different size which are opened when fluid flow is reversed. Such an arrangement requires the use of various parts to control the opening and closing of such passages, as well as machining and assembly considerations in incorporating such parts in the tool. Thus, such known arrangements are expensive.